Recent progress in the treatment of certain diseases of the heart may require better visualization than is afforded by what has been the standard form of visualization, or imaging of the heart. The standard form of imaging has been x-ray, or x-ray fluoroscopy which has a number of disadvantages. Imagining by use of ultrasound offers a number of advantages, primarily surrounding better anatomical images. Recent progress in economically reducing the size of connecting cables to an ultrasound transducer allows for the cabling to be put through a small plastic tube, or catheter, so the ultrasound probe can be inserted percutaneously into the body. Closer proximity to the heart can provide better visualization, with higher resolution, of the desired anatomy. See, for example, U.S. Pat. No. 5,713,363 and Pending U.S. application Ser. No. 09/263,755 filed Mar. 5, 1999 assigned to the Assignee of the present application.
An ultrasound transducer is a piezoelectric material that essentially converts electrical voltage to a sound wave. In intracardiac imaging, the transducer would be placed at the distal top of a catheter, and the transducer then could be inside the heart, to send and receive the sound waves. Used with higher power, such as that used with color doppler imaging, and for a lengthy period of time, it is possible that the transducer, and hence, catheter tip, may heat up, and such heat may be well above a safe body temperature. While computer software can be used to regulate the amount of power put into the catheter, a software malfunction could result in too much power being delivered. It is, therefore, desirable to have a safety cut-off mechanism or other control to avoid such a problem.
Actual temperature monitoring near the top or tip of the catheter is most desirable, with feedback to the computer, with an automatic warning or shut down based upon some upper pre-determined temperature limit. The safety standard set out in the U.S. FDA guidelines is 430° C. although this may vary depending on the environment in which the catheter is being used.
Another problem with ultrasound imaging with a catheter, especially with a multi element array, is that the cabling from the ultrasound machine to the catheter, and from the catheter proximal connector to the catheter transducer housed at the distal tip, is expensive. A first solution to keep the expense low, is to move the ultrasound machine next to the bed, and plug the relatively short catheter directly to the ultrasound machine. This is impractical, as most catheter rooms are sterile or semi-sterile environments, and the machine may have to be some distance for the patient bedside. Thus, a connecting cable which is reusable (and probable non-sterile) is desirable, as opposed to the catheter itself, which is sterile and usually not re-usable. It would be most desirable if this connecting cable could be used as a universal cable in that it could be used with many ultrasound machines. Many ultrasound machines have a standard 200 pin ZIF connector, but most ultrasound machines do not have patient isolation built in to the degree necessary for percutaneous catheter use.